51.4 Garbage in the Text

If C-l shows that the text is wrong, first type C-h l
(view-lossage) to see what commands you typed to produce the
observed results. Then try undoing the changes step by step using
C-x u (undo), until it gets back to a state you consider
correct.

If a large portion of text appears to be missing at the beginning or
end of the buffer, check for the word ‘Narrow’ in the mode line.
If it appears, the text you don't see is probably still present, but
temporarily off-limits. To make it accessible again, type C-x n
w (widen). See Narrowing.